If the Ducks retain 50% on Gibson and sign a $1m backup like Reimer, the Ducks would be paying $4.2m per year. Over the rest of this year and each of the next two years, that's roughly $12.6m, which is about 2/3 of what they'd be spending to keep Gibson.
I know they don't need the cap space right now, but I'm pretty sure the ownership group still likes money, and would mind putting an extra $6.4m in their pockets.
On the other hand, when the best selling point for Gibson is that he "has the potential to be" as good or better than other backups who can be signed for $1m, even $3.2m for the next 2+ years seems like a pretty big gamble for any team acquiring him. That's probably why the Avs only asked about Gibson before they made the smarter move and claimed Kahkonen off waivers.